Conventionally, users of computing devices, such as personal computers, utilize computer cards which are inserted into the host computer to provide hardware expansion or peripheral functions. For example, computer cards may provide memory expansion, data storage, or input/output functions. Many of these computer cards are manufactured in accordance with PCMCIA (Personal Computer Memory Card International Association) standards and are therefore referred to as PCMCIA cards. PCMCIA cards utilize a standardized sixty-eight (68) pin interface for easy interchangeability between different host computers.
Computer cards typically include a battery to provide power for retention of information in memory and for peripheral operations, such as input/output functions. Because the computer cards are relatively small in size, the battery, such as a lithium cell, is usually very small, resulting in limited battery capacity. When the battery voltage drops below a predetermined threshold, a pin of the interface is held low by a controller within the computer card. When the computer card is coupled to a host computer, the computer recognizes the low pin voltage as an indication of low battery voltage. Thereafter, a message may be displayed by the computer to alert a user as to the low voltage condition of the battery. Additionally, some computer cards are capable of generating an audio wave form to drive a host computer's loudspeaker when the battery voltage drops below the threshold. In this manner, the user is conveniently alerted by an audible tone.
However, most computer cards, such as PCMCIA cards, are unable to independently alert a user of a low battery condition. As a result, a low battery condition cannot be recognized by the user unless the card is coupled to a host computer. This is not typically a problem in computer cards that are employed solely for purposes of memory expansion, as memory expansion cards are usually intended to remain coupled to the host computer. Furthermore, memory expansion cards generally consume only minimal amounts of current. Therefore, the battery utilized by memory expansion cards may last several years.
In computer cards providing peripheral functions, however, current is typically consumed at a much higher rate, thereby significantly decreasing the life of the battery. Additionally, some peripheral cards, such as radio frequency (RF) modems, are intended to function when detached from the host computer. As a result, there is a risk that a low battery condition could occur when such a peripheral card is detached from the host computer. Because, as described ,above, typical computer cards are unable to independently alert a user to a low battery condition, the low battery condition could go unnoticed by the user for a long period of time during which the computer card is not coupled to the computer. If this occurs, the battery voltage could drop too low to power the computer card, thus inconveniently causing the loss of any information residing in the memory of the computer card.
Thus, what is needed is a computer card, such as a PCMCIA card, which is able to independently provide a low battery indication to a user.